The resolution of an image photographed by, for example, a digital camera is often degraded in the periphery of the image. In particular, the resolution in the periphery tends to degrade with respect to a central portion around an optical axis due to the dependence of an angle of view of an aperture size or aberration of a lens optical system. The vignetting of an aperture is regarded as one of the causes of degradation. A circular-shaped radial aperture formed in the circumferential direction is vignetted to form an elliptical aperture at an area where an angle of view is wide and thus, an image becomes blurred. As a result, the resolution in radial direction is degraded.
Regarding the degradation of resolution, there is a technique in which an image is filtered using different filter data according to a target position of the image to be corrected, for example, in order to cope with the change of a PSF (Point Spread Function) according to the angle of incident light. See, for example, Japanese Laid-Open Patent Publication No. 2012-23498.
The level of resolution tends to be different depending on a direction and the property is referred to as anisotropy in resolution. For example, the level of resolution in the radial direction around an optical axis is different from that in the circumferential direction.
While a different filtering is performed according to the position of an image in conventional techniques to correct the blur of the image, anisotropy in resolution may not be improved in the conventional techniques.